A turbomolecular pump is used in an etching process such as semiconductor production or the like, or in a CVD process. When particles of a reaction product or the like flow into the turbomolecular pump from a vacuum chamber that is used in those processes, these particles are struck by the rotor that is rotating at high speed and bounce off it, and sometimes it happens that these recoil particles get as far as the vacuum chamber. As a result, there is the problem that the recoil particles adhere upon the wafer, and cause the yield rate of semiconductor production to be deteriorated.
As a structure for reducing this type of reverse flow of recoil particles to the vacuum chamber, structures like those proposed in Patent Documents #1 through #3 have been proposed. In Patent Document #1, a small chamber for capturing particles is provided at the inner peripheral surface of the pump casing, and particles are struck by the rotating blades and bounce off in the direction of this small chamber. And, in Patent Document #2, within the pump casing, it is arranged to provide a capture member made from a rubber material, a sponge material, a cotton material or the like, or a shock absorption member whose coefficient of restitution is small. Furthermore, in Patent Document #3, a flocculent mass made from stainless steel felt or a fluoroplastic resin felt is provided as a particle capture mechanism.